(1) Field of the Invention
This invention relates to a new method of imparting wrinkle resistance, smooth drying properties and abrasion resistance to textiles made of cotton fibers or blends of cotton with polyester.
(2) Description of the Prior Art
Although many types of chemical treatment have previously been recommended to render cotton textiles wrinkle resistant in the dry state at ordinary humidity, and to make cotton textiles smooth drying when laundered in the wet state and then dried, without exception these treatments have greatly lowered the strength, abrasion resistance, and laundering life of the cotton. As a consequence, textile mills have found it necessary to introduce chemically inert synthetic fibers as blends with cotton in the manufacture of wearing apparel and bedsheets in which smoothness and wrinkle-free appearance are important. In textiles where the superior comfort and moisture absorption of cotton make its use necessary at levels as high as 60%-100% in the fabric, the conventional durable press treatments with dimethyloldihydroxyethyleneurea cause the cotton cellulosic fibers to become weakened and embrittled so that a few machine launderings produce ragged and frayed edges in garment cuffs and collars, worn or frosted lines and holes in creases, and thin areas in sheets.
Recently an important advance in overcoming this loss of abrasion resistance and strength during durable press finishing of cotton has been reported by Rowland et al, Textile Research Journal 48, 73-80 (1978) and U.S. Pat. No. 4,255,149 Mar. 10, 1981). Using ammonium persulfate as the free radical initiator in the presence of an alkali metal phosphate, they were able to graft polymerize N-methylolacrylamide on cotton fabric to impart high levels of wrinkle resistance and durable press performance with retention of high flex abrasion resistance and high resistance to weight loss during Accelerator abrasion. Breaking and tearing strength losses were also reduced somewhat.
A major difficulty in any attempt at commercial scale use of their process is that the heat curing step "caused pronounced discoloration of fabric" if carried out in air. To prevent this they found it necessary to heat cure the fabrics wrapped in a plastic bag filled with nitrogen. Moreover, on a lightweight fabric such as 3.2 oz/yd.sup.2 printcloth, heat curing in air noticeably reduced the strength. With most existing mill equipment, heat curing of fabric under a nitrogen atmosphere would be impracticable on a commercial scale. Atmospheric oxygen was suggested as being disadvantageous during heat curing.
However, earlier studies by Frick et al (American Dyestuff Reporter 59 [12] 40-42, 44, 50 (1970)) showed that ammonium persulfate itself produced degradation of cotton cellulose and large fabric strength loss when used as the initiator in the free radical polymerization of acrylamide on cotton fabric by heat curing in air. Heat curing the fabric in a nitrogen-filled bag increased the polymer yield and process reproducibility, but did not decrease fabric degradation. The degradation was caused by reaction of the ammonium persulfate initiator as an oxidizing agent to form "active" or free radical sites directly on cellulose.
Also related to the present invention is the discovery of Wolfram et al (American Dyestuff Reporter 56 [4] 110-116 (1967)) that tetrakis(hydroxymethyl)phosphonium chloride (THPC) acts as an oxygen scavenger in aqueous solution, and when present in catalytic amounts together with a persulfate salt which serves as the polymerization initiator, THPC permits vinyl and acrylic monomers to be polymerized in situ in the fibers of wool textiles even in an oxygen-containing atmosphere which normally would inhibit or retard the polymerization. Wolfram et al observed, however, that in the absence of persulfate initiator, no polymerization occurred even with THPC present. Thus, the phosphonium salt, THPC, is not an initiator of free radical polymerization of vinyl or acrylic monomers, but does act as an accelerator by removing atmospheric oxygen which acts as an inhibitor of the polymerization.